Reductions in maize root-tip elongation by salt and osmotic stress do not correlate with apoplastic O2- levels

DOLORES A. BUSTOS; RAMIRO LASCANO; ANA LAURA VILLASUSO; ESTELA MACHADO; MARÍA EUGENIA SENN; ALICIA CÓRDOBA; EDITH TALEISNIK

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2008 vol. 102 p. 551 - 559

0305-7364

Background and Aims: Experimental evidence in the literature suggests that superoxide produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic superoxide. Methods: Stress treatments were imposed using 150 mM NaCl or 300 mM sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic superoxide was determined using nitro blue tetrazolium, and H2O2 was determined using 20, 70-dichlorofluorescin. Key Results: In non-stressed plants, the distribution of accelerating growth and highest superoxide levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but superoxide levels increased in sorbitol-treated roots and decreased in NaCl-treated roots. Conclusions: The lack of association between apoplastic superoxide levels and root growth inhibition under hyperosmotic stress leads us to hypothesize that under those conditions the role of apoplastic superoxide may be to participate in signalling processes, that convey information on the nature of the substrate that the growing root is exploring.